1. Field of the Invention
The present invention relates to an electromagnetic molten metal supply system more, particularly, the invention relates to an electromagnetic molten metal supply system for maintaining the surface height of molten metal in a molten metal maintaining furnace to a fixed height by controlling a dip type of cylinder electromagnetic pump and reducing variation of the quantity of the molten metal supplied.
2. Description of the Related Art
As a conventional electromagnetic molten metal supply system, the one having the structure illustrated in FIG. 2 has been known. Referring to FIG. 2, in the molten metal maintaining furnace 1 in which a fixed quantity of molten metal is contained, a dip type cylinder electromagnetic pump 2 is disposed. The exciting current to be supplied to an exciting coil 3 of the electromagnetic pump 2 is regulated by a controller 4 and a molten metal surface detecting signal is supplied from a molten metal surface detecting instrument 5 to this controller 4. Further, the electromagnetic pump 2 is connected to a molten metal supply tube 6, the supply outlet of which is communicated with the injection sleeve 7 of a die cast machine. The reference numeral 8 in FIG. 2 is an injection plunger of the die cast machine.
In the above structure, the exciting current for maintaining the molten metal surface at a certain level is supplied from the controller 4 to the excitation coil 3 of the electromagnetic pump 2 in response to the output signal supplied from the molten metal surface detecting instrument 5, thereby the water head H between the level L1 of the molten metal surface in the molten metal supply tube 6 and the molten metal surface level of the furnace 1 is controlled so as to be constant. On the other hand, in a molten metal supply cycle, by changing the current being supplied to the exciting coil 3 through the controller 4, the molten metal is supplied up to a predetermined level L2 of the injection sleeve 7. Moreover, the molten metal thus supplied is injected in the die cavity to the die cast machine (not shown) by the displacement of the injection plunger 8.
Thus, since the conventional electromagnetic molten metal supply system is designed to change the current directed to the exciting coil 3 alternatively when controlling the molten metal surface level of the furnace 1 and controlling the molten metal supply quantity, it is difficult to keep the molten metal surface level constant with accuracy while supplying the molten metal, which has caused the variation of the supply quantity and the deterioration of the molding stability of the die cast products.
To solve the above problems, it may be attempted to employ a furnace where the molten metal surface is kept constant or to maintain the molten metal surface constant with the provision of a separate electromagnetic pump. In this case, however, a considerable increase in equipment cost becomes unavoidable.